Computer displays and televisions are known to utilize different display techniques; computer displays utilize a progressive display technique, while televisions utilize an interlaced technique. The progressive display technique creates fields for displaying wherein each field includes complete pixel information for the display. For example, if the computer display is a 640.times.480 pixel display, each line of a field would include the appropriate pixel information for display. Thus, each field displayed, which is done at a refresh rate of the computer display (e.g., 60 hertz, 75 hertz, 90 hertz, etc.), is complete. Because each field contains complete pixel information, no human perception filtering is required.
The interlaced technique has two types of fields; even fields and odd fields. An even field contains only the pixel information for even lines, while the odd field includes only pixel information for odd lines. As such, both fields are incomplete. When displayed at the refresh rate of the television, which may be approximately 60 hertz in North America, the fields are presented at a rate of 30 even fields and 30 odd fields per second. Because the interlaced display technique alternates between even fields and odd fields, the human visual process filters the fields such that complete images are perceived by the viewer.
As one would expect, a video source designed for display on a television is not directly presentable on a computer display. Such video sources include video cassette records, broadcast television, cable television, satellite television, etc. To present interlaced video data on a progressive computer display, the missing lines must be filled in for each field.
One such technique for filling in the missing lines is referred to as "bob." The bob technique fills in the missing lines of a particular field by calculating the missing data from the image data of the lines that are present on a given field. This technique works well for moving images but, for still images, creates fuzzy edges of the images, which degrades the video quality.
Another technique for completing the missing lines is referred to as a "weave" technique. The weave technique utilizes multiple fields to create the missing lines. This technique works well for still images but, for moving images, creates jagged edges.
Yet another technique is to fill the missing lines in with black image data. (For pixel information the black image data would be all zeros.) By filling in the missing lines with black data, the progressive display resembles television, in that, each field (odd or even) contains less than all of the image data. When presented on the progressive display, at a 60 hertz rate, the human eye filters the even and odd fields such that it perceives a single object. This technique, however, reduces the resulting intensity of the display by a factor of two compared to the bob or weave technique. Thus, images presented on a progressive display are less intense than intended, thereby reducing the video quality.
Therefore, a need exists for a method and apparatus that allows interlaced video data to be presented on a progressive display with minimal adverse visual effects.